1. Field of the Invention
The present invention relates to an optical instrument having a plurality of spaces formed in the optical path of energy beams, and a gas replacement method and cleaning method thereof. More specifically, the present invention relates to an optical instrument used for an exposure apparatus for manufacturing electronic devices such as semiconductor devices, liquid crystal display devices, imaging devices (CCD or the like), and thin film magnetic heads, and a gas replacement method and a cleaning method of the optical instrument. The present invention also relates to an exposure method using the exposure apparatus and a manufacturing method for devices.
2. Description of the Related Art
When semiconductor devices or liquid crystal display devices are manufactured by a photolithography process, a reduction projection exposure apparatus is used, wherein a pattern image of a reticle is reduced in size and projected onto each projection (shot) area on a wafer, on which a photosensitive material (resist) is applied, via a projection optical system. The circuit in the semiconductor device is transferred by exposing the circuit pattern onto a wafer by the projection exposure apparatus, and is formed by post-processing. Integrated circuits are obtained by laminating the circuit wiring formed in this manner repeatedly, for example, through 20 layers.
Recently, integrated circuits have been integrated in high density, that is, miniaturization of circuit patterns has been advanced. Therefore, the exposure light used for the projection exposure apparatus also tends to have a short wavelength. That is to say, a KrF excimer laser (xcex=248 nm) is now being used, instead of the bright-line of a mercury lamp which has heretofore been the mainstream, and implementation of an ArF excimer laser (xcex=193 nm) having a shorter wavelength is now entering the final stage for practical use. Moreover, research of an F2 laser (xcex=157 nm) has been made, aimed at further high-density integration.
In general, ultraviolet radiation having a wavelength of about 190 nm or less is referred to as vacuum-ultraviolet light, and is not transmitted through the air. This is because light is absorbed by substances such as oxygen molecules, water molecules, and carbon dioxide molecules contained in the air (hereinafter referred to as xe2x80x9clight-absorbing substancesxe2x80x9d). Accordingly, with exposure apparatus using the vacuum-ultraviolet light, light-absorbing substances in the exposure optical path should be reduced or eliminated, in order that the exposure light reaches the wafer face with sufficient illuminance.
Moreover, with an exposure apparatus using the KrF excimer laser beam or the ArF excimer laser beam, there is a problem of a phenomenon referred to as xe2x80x9ccloudingxe2x80x9d of optical members. This is a phenomenon where contaminants adhere to the optical member and cause absorption. Due to this xe2x80x9ccloudingxe2x80x9d, it becomes difficult for exposure light having sufficient illuminance to reach the wafer, thereby decreasing the throughput. As the contaminants causing xe2x80x9ccloudingxe2x80x9d, there can be considered halides such as plasticizers contained in the covering material of electric wires, exposed to the space where the exposure optical path is formed, organic substances such as machine oil adhered to members constituting the apparatus, or organic substances contained in adhesives or the like.
Currently, measures are taken such that, for non-metal members of the members constituting the exposure apparatus, a substance having less outgassing is used, and for metal members, a substance having low surface roughness is used, the machine oil is completely removed by means of ultrasonic cleaning or the like, and these members are stored in a closed space purged by dry nitrogen. However, it is not easy to prevent outgassing completely, nor to remove the xe2x80x9ccloudingxe2x80x9d completely, and contaminants causing xe2x80x9ccloudingxe2x80x9d adhere to the optical members even during assembly of the apparatus or during operation (during shading pattern exposure).
Therefore, in order to irradiate the exposure light stably onto the substrate, it is necessary to eliminate the light-absorbing substances from the exposure optical path all the time, and to regularly clean the optical members.
With a conventional exposure apparatus, in order to make the exposure light reach the substrate with sufficient illuminance and uniformly, efforts have been made involving replacing the inside of the exposure optical path with low absorbent gas having little energy absorption of vacuum-ultraviolet light, to thereby reduce the light-absorbing substances in the exposure optical path. However, in the case of optical instruments using vacuum-ultraviolet light, since the light is apt to be absorbed by the light-absorbing substances, as described above, it is necessary to keep the concentration of light-absorbing substances contained in the gas within the exposure optical path as low as possible, for example, less than about several ppm. The replacement gas is generally expensive, and the consumption thereof is a problem associated with the running cost of the apparatus. With optical instruments using vacuum-ultraviolet light, since all of a plurality of spaces forming the exposure optical path must be subjected to the gas replacement, the running cost for the gas replacement is large, and its reduction is an important problem. Moreover, in order to replace all the spaces with the replacement gas effectively, without decreasing the operating ratio of the apparatus, it is necessary to reduce the light-absorbing substances in the individual spaces within as short a time as possible. Furthermore, since the rate at which the light-absorbing substances are generated and the inflow quantity are different for each individual space, it is necessary to take measures depending on these spaces.
Also, there has heretofore been a technique for removing contaminants adsorbed in the optical members, referred to as optical cleaning (or light ozone cleaning). With optical cleaning, oxygen gas absorbs ultraviolet light, and is excited to become ozone. Then, the oxygen gas is further converted to oxygen atoms having high reactivity, to react with contaminants adhered to the optical members, and becomes light molecules such as water, carbon dioxide, and is removed. From research up to now, it is known that optical cleaning has low effectiveness where there are no oxygen molecules (J. Illum. Engng. Inst. Jpn. Vol. 83, Nov. 5, 1999, xe2x80x9cVerification of UV/03 Cleaning Using Xe2 Excimer Lampxe2x80x9d). Since the absorption cross section (absorption coefficient) of substances in the vacuum-ultraviolet light is larger than the case of ultraviolet light having a longer wavelength, it is obvious that with an optical instrument using vacuum-ultraviolet light, more reliable measures against xe2x80x9ccloudingxe2x80x9d are required.
However, in the case of light having a low wavelength such as the F2 laser, since the energy is apt to be absorbed by the light-absorbing substances, if the light-absorbing substances are contained in a large amount in the gas within the exposure optical path, the light hardly reaches sufficiently to the space located away from the light source in the optical path, and hence effective optical cleaning cannot be performed with respect to the optical members. Also, in the case of vacuum-ultraviolet light, there is the contradiction that, in order to transfer a pattern with sufficient light volume, it is necessary to eliminate the oxygen molecules, which are light-absorbing substances, but oxygen molecules are necessary for the optical cleaning.
As described above, the vacuum-ultraviolet light is difficult to handle, and considerable labor is required for keeping cleanliness. Consequently, a cost increase, and a decrease in throughput cannot be avoided.
In view of the above situation, it is a primary object of the present invention to provide an optical instrument which can reduce the concentration of light-absorbing substances and the concentration nonuniformity in the optical path effectively, with reduced gas consumption or within a predetermined time, and a gas replacement method for the optical instrument.
An other object of the present invention is to provide an optical instrument which can reliably clean optical members arranged on the optical path, even if vacuum-ultraviolet light is used, and a cleaning method thereof.
It is an other object of the present invention to provide an exposure method, a manufacturing method for devices and an exposure apparatus, which enables highly accurate exposure, without a cost increase nor any decrease in throughput.
With the present invention, in order to solve the above problems, the construction described below is adopted. That is to say, when explained in association with the drawings, the present invention is characterized by an optical instrument having a plurality of spaces formed in an optical path of an energy beam IL, which comprises a gas replacement apparatus 54 for selectively replacing the gas in at least one of these plurality of spaces. Here, xe2x80x9cspacexe2x80x9d stands for a three-dimensional area surrounded by an object, for example, an internal space of a housing, including either of the space having an airtight structure which is airtightly isolated from an outside air or the space which is applied pressure higher than that of the outside for escaping gas in the space to the outside.
In this case, the optical instrument may have a light source 20 for emitting the energy beam IL, and a control unit 23 which controls the light source 20 and the gas replacement apparatus 54, so that while a predetermined energy beam IL is emitted towards the space on the light source side, among the plurality of spaces, the gas in the plurality of spaces is replaced from the space on the light source side, sequentially along the traveling direction of the energy beam.
Moreover, the gas replacement apparatus 54 may comprise a gas supply device 55 for supplying a predetermined gas to the plurality of spaces, respectively, and a gas exhaust device 56 for exhausting the gas in the spaces, respectively, from the plurality of spaces.
The gas supplied from the gas supply device 55 may also contain an ozone substance or substances which absorb the energy beam IL and generate ozone.
The gas supply device 81 may also comprise a stirring device for stirring the gas in the plurality of spaces.
A supply port 85 and an exhaust port 86 of the gas are arranged, with their height changed from each other, so that the gas in the space is replaced due to a difference of specific gravity between the gas supplied to the space and the gas in the space.
The control unit 23 has at least one of a first measuring device 75 for measuring a concentration of impurities in the gas in the space, and a second measuring device for measuring optical information of the energy beam IL having passed through the plurality of spaces, and either one of the plurality of spaces may be selectively subjected to gas replacement, based on the measurement results of the first and second measuring devices.
Moreover, the present invention is a gas replacement method for an optical instrument having a plurality of spaces formed in an optical path of an energy beam IL from a light source, wherein the predetermined energy beam IL is emitted toward the space on the light source side among the plurality of spaces, and the plurality of spaces are subjected to gas replacement from the space on the light source side, sequentially along the traveling direction of the energy beam IL.
An exposure apparatus 10 of the present invention is also characterized in that at least one of an illumination optical system LO for illuminating a mask R having a pattern formed thereon with an energy beam IL, and a projection optical system PL for transferring the pattern on the mask onto a substrate, is constituted of the above described optical instrument.
The present invention also relates to an exposure method for irradiating light IL, having a first wavelength onto a mask R, and transferring a pattern on the mask onto a substrate W under this light having the first wavelength, wherein before the transfer, optical members 30, 31, 32 arranged in the optical path of the light IL having the first wavelength are irradiated with light CL having a second wavelength longer than the light IL having the first wavelength, to thereby optically clean these optical members.
The present invention also relates to an exposure apparatus for irradiating light IL having a first wavelength to a mask R, and transferring a pattern on the mask onto a substrate W under this light having the first wavelength, which comprises an optical cleaning mechanism 1 which irradiates light CL having a second wavelength longer than the light IL having the first wavelength onto optical members 30, 31, 32 arranged in the optical path of the light IL having the first wavelength, to thereby optically clean these optical members.
The cleaning method of the present invention is a cleaning method of optical members 30, 31, 32 arranged in the optical path of the light IL having the first wavelength, in an exposure apparatus for transferring a pattern on a mask R onto a substrate W under this light having the first wavelength, characterized by irradiating light CL having a second wavelength longer than the light IL having the first wavelength onto the optical members, to thereby optically clean these optical members.
Moreover, the manufacturing method for devices according to the present invention is a manufacturing method for devices manufactured through a transfer step for transferring a pattern of a mask R onto a substrate W under light IL having a first wavelength, characterized by comprising a step, prior to the transfer step, for irradiating light CL having a second wavelength longer than the light IL having the first wavelength onto optical members 30, 31, 32 arranged in the optical path of the light IL having the first wavelength, to thereby optically clean these optical members.